The invention relates to infrared radiation detectors and, more particularly, to a system and method for generating signals representing infrared radiation.
An infrared radiation detector responds to the thermal energy radiated by objects, such as animals, automobiles, and airplanes. This thermal energy is typically not visible to the human eye. Accordingly, by using an infrared radiation detector, objects that are not visible may be perceived and/or alternative views of visible objects may be obtained.
An infrared radiation detector may have a single detector element or an array (linear or two-dimensional) of detector elements. The detector elements produce electrical signals in response to infrared radiation, and the electrical signals are processed to produce useful information. For a single detector element observing a moving object, the processing typically relies on a fairly large alternating current (AC) coupling capacitor to remove the direct current (DC) bias component. For linear arrays of detector elements observing a moving object, a similar approach may be used because very few space restrictions exist in the scan direction. Moreover, the transconductance (the ratio of the input current to the output voltage) may be set low by using a capacitor with a large capacitance, which requires a fairly large capacitor. In addition, a large capacitor provides a single-pole filter to minimize noise. This same approach can be used for two-dimensional arrays observing a moving object, as long as the pitch (the spacing between the center of the pixels) is in the range of one-hundred microns.
Unfortunately, these techniques have several disadvantages when trying to apply them to a two-dimensional array that observes a relatively stationary scene. For example, using an AC coupling capacitor requires a high capacitance in order to observe slow moving objects. Such a capacitor would require a large amount of space, which may not be available in a two-dimensional array. Moreover, these techniques may be unable to observe a stationary scene. Typically, two dimensional arrays suffer from a combination of the following drawbacks, performance significantly below the theoretical detector limit, substantial production cost, and large pixel pitch.
The present invention provides systems and methods that substantially reduce or eliminate at least some of the disadvantages with the prior art. Accordingly, at least in certain embodiments, the present invention provides a system and method for generating signals representing infrared radiation detected by a small pitch, two-dimensional array of infrared detector elements observing a relatively stationery scene.
In certain embodiments, a system for generating signals representing infrared radiation includes a plurality of infrared detector elements and a system for determining the output of the detector elements. The infrared detector elements are arranged in a two-dimensional array and biased so that they produce a signal even when no infrared radiation is impinging thereon. The detector elements are operable to receive infrared radiation from a reference scene and an actual scene. The system for determining the output of the detector elements includes a bias signal remover, a signal attenuator, a signal integrator, and a signal sampler. The bias signal remover is operable to receive a first signal representing the reference scene from one of the detector elements and a second signal representing the actual scene from the detector element and remove the bias signal from the second signal. The signal attenuator is coupled to the bias signal remover and is operable to attenuate the remaining second signal. The signal integrator is coupled to the signal attenuator and is operable to integrate the attenuated signal. The signal sampler is coupled to the signal integrator and is operable to sample the integrated signal.
In particular embodiments, a method for generating signals representing infrared radiation includes providing a reference scene and an actual scene to a plurality of infrared detector elements arranged in a two-dimensional array, the detector elements being biased so that they produce a signal even when no infrared radiation is impinging thereon. The method also includes receiving a first signal representing the reference scene from one of the detector elements, receiving a second signal representing the actual scene signal from the detector element, and removing the bias signal from the second signal. The method additionally includes attenuating the remaining second signal, integrating the attenuated signal, and sampling the integrated signal.
The present invention has several technical features. For example, in particular embodiments, the invention allows autozeroing of detector elements"" bias currents on an element by element basis. Accordingly, the invention is useful for arrays where the resistance of the detector elements varies. As another example, in certain embodiments, the invention can be implemented in limited space. Thus, the invention is useful for two-dimensional arrays of detector elements where spacing is confined. Moreover, this may enhance fill factor for the detector elements. As a further example, in some embodiments, the invention provides for integration of the signal from the detector elements, which allows for increased signal-to-noise ratio. As a still further example, in certain embodiments, the invention allows operation without cooling of the detector elements, which simplifies operation of the invention. As another example, in some embodiments, the invention provides a good dynamic rangexe2x80x94the ratio between the point at which the detector saturates and the point at which the detector first begins to detect IR radiationxe2x80x94to be achieved. Thus, the invention allows a wide range of IR radiation to be detected. As still another example, in some embodiments, the invention is implementable using CMOS technology. Accordingly, the invention may be readily manufactured at reasonable cost. Of course, some embodiments may contain one, some, or all of these technical features.
Other technical features will be readily apparent to those skilled in the art from the following figures, written description, and claims.